October 27, 2009--Don't be fooled by the kindly eyes and half smiles. What you're looking at here are potential frozen zombies, aka wood frogs.

Frighteningly well adapted to their chilly northern North American habitats, wood frogs are among the animal world's "zombies"--Halloween-y creatures that've evolved the ability to twitch back from the brink of death.

Lab tests have shown wood frogs to survive being frozen nearly solid--with up to 70 percent of their internal water turned to ice--for about four weeks, usually in forest burrows, according to researchers at the Laboratory for Ecophysiological Cryobiology at Miami University, Ohio. The frogs' resilience is linked to a shifting of water to areas less likely to be damaged by freezing, as well as natural "antifreeze" in their blood.

During thawing, wood frogs' hearts begin beating again, and normal movement returns within about a day, scientists say.

--Ted Chamberlain

MORE ON WOOD FROG "ZOMBIES"
• Frozen Frog May Give Docs Jump on Human Transplants
• Antifreeze-Like Blood Lets Frogs Freeze and Thaw With Winter's Whims